The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus and more particularly, to a fixing device included therein.
A fixing device of the type including a heat roller and a press roller is customary with an image forming apparatus. The prerequisite with this type of fixing device is that the heat roller and press roller have a high parting ability. A low parting ability would cause part of the toner to adhere to the heat roller or the press roller and would thereby bring about offset. In light of this, there has been proposed a fixing device including a heat roller and a press roller each having a parting layer on its circumferential surface, and an applicator roller for applying silicone oil to the parting layer.
Even the above fixing device using the parting layer and applicator roller scheme cannot fully obviate offset. Specifically, a small amount of offset remains on the heat roller or the press roller and causes toner and paper dust to contaminate the surface of the applicator roller. In addition, the amount of oil to be applied by the applicator roller decreases due to aging, or the surface of the applicator roller is contaminated. The contamination of the applicator roller is retransferred to the heat roller or the press roller, resulting in the contamination of a paper or similar recording medium.
To solve the above retransfer problem, Japanese Patent Laid-Open Publication No. 7-234600, for example, discloses a fixing device including an applicator roller having a unique configuration (Prior Art 1 hereinafter). The applicator roller of Prior Art 1 is made up of a base formed of a foam material and a surface layer formed of the same material as the parting layer of a heat roller or that of a press roller. Specifically, the surface layer is formed of fluorocarbon resin and formed with a number of pores. The base is impregnated with silicone oil. A cleaning member is used to clean the surface of the applicator roller.
Japanese Patent Laid-Open Publication No. 9-6173 teaches a fixing device includes a cleaning roller for cleaning the surface of an applicator roller and a blade for removing impurities from the circumferential surface of the cleaning roller (Prior Art 2 hereinafter).
The problem with Prior Art 1 is that the cleaning roller is contaminated due to aging and, in turn, contaminates the heat roller, as stated earlier. Prior Art 2 has a problem that some paper dust is passed through a gap between the cleaning roller and the blade, also resulting in the contamination of a paper. Today, a filler, for example, is added to papers for promoting recycling or enhancing whiteness. The filler, however, increases the amount of paper dust to be collected by the applicator roller and cleaning roller. Such paper dust causes impurities collected by the cleaning roller to remain on the applicator roller due to the viscosity of toner, lowering the ability of the applicator roller and image quality.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-76628 and 9-6173.